Stabilizing the world’s climates means cutting carbon dioxide pollution. There’s no way around it. But what if that’s not enough? What if it’s so late in the game that even cutting carbon emissions to zero, tomorrow, wouldn’t do? Enter solar geoengineering. The principle is simple: attempt to cool Earth by reflecting more sunlight back into space. The primary mechanism, shooting particles into the upper atmosphere, implies more pollution, not less. If that doesn’t sound scary, it should. There are lots of risks, unknowns, and unknowables. In Geoengineering: The Gamble, climate economist Gernot Wagner provides a balanced take on the possible benefits and all-too-real risks. Despite those risks, he argues, geoengineering may only be a matter of time. Not if, but when. As the founding executive director of Harvard’s Solar Geoengineering Research Program, Wagner offers an inside view of the research already under way, and the actions the world must take to guide it in a productive direction. He lays out realistic scenarios of a geoengineered future and the pathways available to steer the world toward a balanced climate policy portfolio.